[burls]

I have just test driven the LJ and the rear brakes lock up way before the fronts. I have read that the drum brake valve may be the issue. I have vitara master cylinder, sierra front and rear discs and all the plumbing straight out of my 95 sierra.. Any thoughts from you brake gurus?

[Matthew]

Brake proportioning valve

[joeblow]

burls wrote:

sierra rear discs

Bingo......there is your issue. Absolute rubbish system.

[Gwagensteve]

Matthew wrote:

Brake proportioning valve

This.

Steve.

[burls]

Then what should I do joe

[got_bar_work]

Find calipers off the rear of a car not the front

[burls]

I will look into the brake pro portioning first before I go down the path of replacing the rears. I am sure this mod has been done many times or you wouldn't be able to buy a kit

[SierraDan]

Proportioning valve is the answer

[burls]

So do I need to repair the one from the sierra or replace it altogether with something else and if so what has been used before

[Scrawny]

Have a read through this thread, similar to what you're up to

viewtopic.php?f=5&t=40106&hilit=Proportioning

[burls]

Yeah found it this morning thanks

I also found something else hmmm in the vitara manual it has the rear chamber hooked up to the front brakes with non abs. Can anyone confirm which chamber on the vitara MC should go to the front and rear?

[shep]

Fit one of these and it will sort the problem.

http://www.ebay.com.au/itm/Adjustable-b ... fe2&_uhb=1

[burls]

Are they legal?

[2stroker]

burls wrote:

Are they legal?

Hmmm, are your rear discs legal

[burls]

Will be as its getting engineered at the end of the month

[joeblow]

A valve that can be adjusted by hand is usually frowned upon. You can hide it but if the engineer spots it he may decide not to do your vehicle. If an engineer drives and does a brake test with the Sierra discs it's going to be a short drive.

I still don't understand why some places offer these as kits. Using a Sierra caliper on the rear is just dangerous.

[burls]

Do you say they are dangerous because they are too responsive? I have to admit I wasn't impressed myself but I thought it would only need tweaking of some sort.

I told the engineer what I was doing when I started and he didn't disagree or ask me to do something else.

[Gwagensteve]

A brake proportioning valve which can't be readily user adjusted by hand should be no problem for the engineer - after all, many vehicles have them from the factory, suspension position changes the proportioning - yet almost no aftermarket suspension kit does anything to correct it.

Sierra front calipers are just fine, they simply need to be proportioned correctly. Fit a prop valve, mounted and/or made tamper proof in accordance with the wishes of the engineer and get on with the job. There's no inherent problem with sierra calipers used in the rear, once proportioned properly.

Steve.

[burls]

Ok thanks Steve

What's the valve half way down on the RHS on the sierra for?

[Gwagensteve]

That's a bit of a weird one that. It's a proportioning valve, per se, but it balances front to rear based on pedal pressure rather than suspension position, which is how most manufacturers do it. You'll note on a WT there's an extra brake line that runs from the front tee down to that prop valve. Front brake pressure is applied to the valve to adjust pressure to the rear brakes.

It won't work to fix the problem with the sierra front calipers. A disc/disc MC helps, but the piston volume won't work all that well - you still need to drop pressure to the rear callipers to get it right with a prop valve.

I'm running Estate wagon front rotors and calipers in the front and sierra front in the rear, with a 1 1/16 Forester GT MC, currently unboosted. It was still squirrelly in 2WD on wet tarmac or dirt. The prop valve allowed me to tune this. I did it on a smooth, flat dry dirt road, and set the car up so the front broke traction before the rear. It's been great since.

Steve.

[burls]

Thanks Steve
I thought I was doing the right thing using all the sierra gear including this so call prop valve. I guess not, I'll talk to the engineer and see what he wants me to do. Should I remove all the sierra stuff and just run a single line to the rear or just put the adjustable valve after the sierra valve

[Gwagensteve]

I'd just use a single line and a manual prop valve, but I agree, talk to the engineer. If he's happy, you'll be happy.

Steve.

[burls]

Back on to this problem
Can someone confirm that the front outlet on the vitara master cylinder goes to the front brakes or the back brakes

[303zuke]

Just about all master cylinders on all vehicles have the first outlet (closest to the pedal/rod) plumbed to the front axle, while the second outlet goes to the rear. The theory is that the front axle system sees an increase in pipe pressure fractionally sooner than the rear.

It should have been the way the donor Sierra was, and also the way your LJ was too.

[christover1]

Tried to check my Vit, but it was a bit hard in the dark.
Some kind of 3 way splitter is confusing.

Mc has single line from outlet closest to firewall.
It joins a splitter, and appears to go to rear.
There is 2 lines to rear, to do with the bias valve at rear possibly.

Has twin outlets at other end, one that heads over to passenger front directly.
Other joins a splitter with an outlet going to drivers front.

[Rhinoman]

burls wrote:

Back on to this problem
Can someone confirm that the front outlet on the vitara master cylinder goes to the front brakes or the back brakes

Its a tandem m/c so front to front, rear to rear, that way the rear brakes start to come on slightly before the front for stability.

[burls]

Haven't heard of a tandem m/c before, is that for a certain vehicle or operation. My vit mc has a twin outlet on the front of which I have blanked one and the other goes to the front sierra splitter. The rear chamber closest to the booster goes to the rear.
Reading the vit manual it says that for abs it's front to rear but if its non abs its front to front.